Warhead - Not that many safe places for humans. If you like infecting people this is your map.
Overdose - Great, fun map for both infected and humans. If your team isn't full of idiots being a human is easy.
Two Towers - Great map for humans. Gigantic map filled with nooks and crannies to hide in.
Showdown - Rather blah. Kind of like turning Overdose inside out. The only safe place for humans being the roof can be infected from underneath. Much easier to be infected here.